US2345887A - Method of sealing containers - Google Patents

Description

April 1944= J. E. ROTHROCK ,3

METHOD OF SEALING CONTAINERS Filed April 5, 1940- JOHN E. ROTHROCK INVENTOR.

BY MM (fi. M Q

ATTORNEY.

Patented Apr. 4, 1944 HNETED STATE$ METHOD OF SEALING CONTAINERS 1 Claim.

This invention relates to containers for explosives and more particularly to ameans of closing plastic containers in a waterproof manher.

The explosive industry has for many years packed its explosives in paper cartridges or paper bags and has supplied blasting caps which are inserted into the explosive to effect priming contact and means of detonating the charge. The use of paper cartridges and blasting caps presents certain problems which are definite disadvantages. Whenever paper containers of nitro-glycerin explosives are handled, the operators in most instances develop severe headaches which are most uncomfortable and reduce their efiiciency. The priming or inserting of blasting caps into the explosive cartridges is a dangerous job at best, and one which requires skill to insure proper priming contact between the blasting cap and the explosive. A further disadvantage of the paper cartridges is their lack of complete waterproofness. This disadvantage of lack of waterproofness is becoming more noticeable due to the increase in the use of ammonium nitrate explosives, since these explosives are very susceptible to water.

To overcome the various disadvantages of paper cartridges, the use of molded plastic cartridges has been developed. The use of plastic containers has provided the explosive industry with a means whereby waterproofness of an explosive has been increased. By packing explosives in a plastic cartridge and sealing this cartridge in a substantially waterproof manner. an assembly is produced in which the operator may place reliance. The assembly may be used undera considerable head of water and the ex- .plosive therein will generally be in proper condition.

The plastic containers while presenting an ad- Vance in the art, present the problem of obtaining a completely waterproof closure. The use of screw joints has not been completely successful and often under hgh hydrostatic pressures, water will find its way into the explosive. An additional disadvantage of the plastic container, is the fact that all of the closures must be fitted into place by a friction. This, of course, is a disadvantage in the explosive art due to safety precautions which must be taken. A further disadvantage ls that frictional positioning usually takes the form of screwing a cover into a threaded container, and such an operation is diflicult to perform safely on an automatic machine. This operation is especially difficult to perform Application April 5, 1940, Serial No. 327,991

on a machine such as the Hall packing machine, commonly used in packing explosives.

It is the object of this invention to provide a means of closing plastic explosive containers in a simple and-efficient manner which will provide a. completely waterproof seal.

A further object of this invention is to provide a closure which is not positioned by frictional methods.

A further object of this invention is to provide a type closure which may be adapted for use on a Hall machine.

A still further object of this invention is to provide a closure which is more economical than the present friction closing devices.

Other objects will appear hereinafter.

In accordance with this invention, these objects have been accomplished by providing a sealing disk which fits into an explosive container prepared from a molded plastic composition. The container may have a small shoulder cut into the open end thereof for receiving a disk of molded plastic. Further, in accordance with this invention, the disk of molded plastic, after it has been inserted into the molded plastic container, is adapted due to its, coefficient of expansion to grip the outside walls of the container and thus give a completely waterproof seal, and thereby form a waterproof assembly.

Described generally, my invention comprises a disk of plastic material having a thermal expansion coefficient sufficiently high so that it may be sized to fit into a tubular plastic container with between about .0005 and about .003 inch clearance around its periphery when the temperatures of the disk and the plastic cartridges are substantially different. For example, my plastic disk, due to its high coemcient of thermal expansion will, when cooled to F. below the temperature of the plastic cartridge, drop readily onto a shoulder or seat in the open end of a plast c cartridge and upon the two pieces of plastics arriving at the same temperature, the disk will, due to its thermal expansion, seize the plastic container in a waterproof manner, and provide a completely waterproof seal.

Having now indicated in a general way the nature and purpose of this invention, there follows a more detailed description of preferred embodL ments thereof with reference to the accompanying drawing in which Fig. l is a cross-sectional View of a plastic explosive container having positioned in the open end portion thereof a plastic disk which provides the plastic explosive container with a completely waterproof seal.

Fig. 2 is a cross-sectional view of an individual disk for closing plastic containers.

Fig. 3 is a fragmental view of an alternative means of positioning the disk into the plastic explosive cartridge.

Fig. 4 is a fragmental view of means of maintaining the disk in position.

Referring now to the drawing and more particularly to Fig. 1, there is shown an explosive container comprising a tubular casing I made from a non-sparking molding material. The casing l is open at one end, and this opening contains interior threads 2 designed to receive and mesh with exterior threads on similar explosive cartridges. Exterior threads 3 are shown adejacent the closed end of the plastic explosive casing I The closure 4 is reduced to a temperature about 50 F. below the temperature of the container and .then is positioned on the seat or shoulder 5, and because of the high thermal expansion coefficient, firmly grips the side walls of the tubular container I when the two materials reach the same temperature. In order to facilitate positioning the disk, I may slightly taper the inside walls leading down to the shoulder 5, but this expedient is not usually found necessary as the decrease in diameter provides sufiicient clearance to allow the easy positioning of the disk onto the shoulder.

If found desirable, the closure 4 may be made with concave or convex surfaces, Fig. 2, depending entirely upon the ease with which molding may be accomplished. An advantage of using a convex surface on the top side of the closure 4 is that upon screwing an additional plastic container into the interior threads of the plastic container, a contact is established between the bottom of the additional container and the top of the convex surfaces which tends to maintain and to force theclosure disk into tight contact with the side walls of the container. The edges of the disk may also be slightly convex or rounded to aid in forming a line contact between the disk and the container. Line contacts are known to be the easiest method of forming tight joints.

While I have found that the closure of this invention may be placed in the plastic container on shoulder 5, and that expansion of the disk will give waterproof contact and p ovide a waterproof container for explosives, I have also found that an alternative method of obtaining this type closure, which has certain advantages, is the filling of the shoulder 5 with a mastic material such as, for example, asphalt, wax, cement, heavy grease, resin and like materials, in a manner shown by dotted lines 6, Fig. 3. This type filling prevents any explosive from lodging on the shoulder 5 and further aids in obtaining a waterproof joint when the closure 4 is dropped or lightly forced onto the shoulder 5. In Fig. 3 the closure 4A is shown by dotted line to indicate its position just before entering the recess formed by shoulder 5, and the closure 4 is also shown by a solid line after it has been positioned. The mastic material which is shown, in place before the closure 4 is positioned, by dotted line B is forced out of the shoulder when the disk is positioned, and aids in making a waterproof joint which is indicated by cross-hatching 1.

Although the use of mastic material in some cases is extremely desirable, I prefer to-use the container without such materials as I find that complete waterproof contact may be had by relying entirely upon the thermal expansion of the closing disk i. The use of the mastic material is r advantageous in preventing the explosive from lodging on the shoulder 5, but actually it does not aid materially in the waterproofness of the container.

Since there is no reason for opening the con tainers once they are filled and sealed, I may use a restraining ledge 8, Fig. 4, to aid in positioning the closure disk 4. This restraining ledge 8 prevents opening or tampering with the container and constitutes a safety feature not enjoyed by other explosive containers.

The moldable plastic materials which I have found useful in forming the closure disk of my invention are of the phenol-aldehyde, urea-aldehyde, thiourea-aldehyde, wood flour, or noncombustible filled phenolics, and ureas, the lignin fiber or lignocellulose plastics, a fibrous base bound with thermoplastic lignin resins, polyvinyl compounds, cellulose acetate, cellulose acetate mixed esters, and chlorinated rubber. The controlling feature of the materials which I have found to be adaptable for closing devices is their thermal expansion coefficient. I have found that the moldable materials with a thermal expansion in the order of about .00002 in./in./degree C. provide a disk which allows insertion into a cartridge when there is a temperature differential of about 50 F. and which upon expansion provides a waterproof seal. An additional feature which affects the choice of the most desirable plastic for use in this invention is the inherent .characteristic of some of the plastics to cold flow. The phenomenon of cold flow must beconsidered in selecting the plastic to be used, but this phenomenon is not extremely serious as it is not experienced with the phenolic, urea, or thiourea resins which are the preferable resins and only exists to a slight extent in the vinyl, and acetate resins. The following table shows the thermal expansion of various suitable moldable materials which are adaptable for use in this invention.

TABLE Thermal expansion Coefficient of Moldable plastic gfig gg C.Xl(H

1. 5 2. 0-3. 0 2. 0-6. 0 2. 5-4. 0 Cast phenolics 2.8 Wood flour phenolics 3. 7-7. 5 Styrene 6. 5-7. 5 Vinyl 6. 9

7. 0-9. 0 Casein 8 Hard rubber 8 itrate l2 -l6 Acetate 14 -l6 Throughout the specification and claims where I have referred to plastic materials, I mean to use the term plastic in the sense that it is used in the molding plas'tic art. Thus, the term plastic refers to organic molded or moldable materials which may be, for example, of the thermosetting or thermoplastic type. However, the type explosive to be packed in the moldable plastic container controls the type plastic which is adapt able for use. Thus, when nitroglycerin explosives are used, plastics which nitroglycerin will plasticize cannot be used for the container. With ammonium nitrate explosives, this diificulty is not encountered. Various moldable plastics which are known to plasticize with nitroglycerin or other similar explosives, for example, the nitro glycols or nitroethyleneglycol are not contemplated for use as explosive containers with compositions containing these liquid explosives. They would, however, be suitable and adaptable for use with the ammonium nitrate type explosive. It is to be understood, therefore, that the moldable plastic container and closure which I intend to use will be selected only after a consideration of the explosive composition to be packed.

In order to show that a waterproof seal may be obtained with the device of this invention, the following specific examples are given.

EXAMPLE 1 A phenol aldehyde cartridge having an inside diameter of about 1.25 inches at the shoulder point, see Fig. l, 5, was maintained at room temperature in condition for closing. A disk of phenol aldehyde composition which is slightly larger, about .001 inch, than the inside diameter of the cartridge at the shoulder point when compared at room temperature, was cooled at about F., and when equalized was dropped into the cartridge where it came to rest on the shoulder 5. The two pieces were then allowed to equalize at room temperature, and, due to the expansion of the closure disk, a tight waterproof joint was formed between the cartridge and disk. In order to test the waterproofness of this joint when the assembly had reached room temperature, hydrostatic pressure was applied on the outside of the joint. The joint maintained its waterproofness under a hydrostatic pressure of 150 feet. This pressure is well above that encountered in normal bore hole blasting and is comparable with those pressures encountered in shooting deep Wells.

The waterproofness of the device is maintained up to pressures where the containendeforms or collapses.

In order to further test the water resistance of the joint, a cartridge was filled with anhydrous copper sulfate, sealed and placed in a room maintained at 100 F. and 100% relative humidity for a period of 72 hours. During this exposure no moisture vapor passed the joint, since the copper sulfate did not develop a blue color, which conclusively shows that the seal is vapor tight and gas tight.

EXAMPLE 2 A cartridge formed of a wood flour filled. phenol-aldehyde composition and having an inside diameter of about 2 inches at the shoulder point, see Fig. l, 5, was maintained at room temperature in condition for closing. A disk of the same composition, which was about .002 inch larger than the inside diameter of the cartridge at the shoulder point when at room temperature, was cooled to about 0 F. and when equalized was dropped into the cartridge where it came to rest on the shoulder 5. The two pieces were then allowed to equalize at room temperature, and, due to the expansion of the closure disk, a tight joint was formed between the cartridge and disk. In order to test the waterproofness of the cartridge when the assembly has reached room temperature, a hydrostatic pressure of 150 feet was applied to the joint for a period of 20 hours. This joint maintained its waterproofness under this hydrostatic pressure. This pressure is well above that encountered in normal bore hole blasting and is comparable with those pressures encountered in seismic prospecting and deep well shooting.

In the above examples, closed end cartridges have been sealed with a disk but, if desirable, due to economic advantages, the cartridges may be molded in the form of a tube with both ends open. closure to each end. The bottom end is usually closed first, the casing filled and the top closed, but this is not essential since the casing may be filled from either end. The disks may be positioned entirely by means of a shoulder or the tubes may be slipped onto a-mandrel for positioning one disk. The use of a mandrel obviates the need of a shoulder in one end of the cartridge, but the use of a shoulder is preferred.

The sealing device of my invention has proved extremely useful in practical application, because it is simple and easy to insert into a plastic cartridge and because it provides an efficient waterproof closing. Thus, when plastic cartridges are filled, for example, on a Hall machine, and the shuttle makes a turn to bring another row of cartridges under the tamping rod, I have found that I may position cooled disks into the open end of the packed plastic cartridges and thereafter allow the temperature to raise by, for example, blowing a stream of hot air on the disk, and that this operation provides a completely waterproof seal for the cartridges. On the next turn of the shuttle, the cartridges are dumped into a receiver and are ready to be taken to the packing house. This method of sealing cartridges is very fast and very efflcient.

The advantages to be gained by this type disk closure are many, for example, the closure may be made without using the friction necessitated by the use of threads. The elimination of friction prevents any hazard which might be inherent in screwing a closure into the open end of the cartridge. A further advantage is that the disk when sealed into the cartridge is very difilcult to remove therefrom and this prevents any attempt to removal when the cartridge is in the field. This provides a safety point which is very much desirable in the explosive industry.

It will be understood that the details-and examples hereinbefore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

The method of producing a filled, waterproof, plastic explosive cartridge comprising a container having a shoulder at one end for receiving a plastic closure member, which method comprises positioning a mastic material on said shoulder in such a manner as to eliminate the obstructing effect of said shoulder while the con tainer is being filled with an explosive, filling that portion of said container below said shoulder with an explosive, and forcing a closure mem ber, which is at a temperature substantially below that of the container onto said mastic-filled shoulder, and permitting said closure member to expand into sealing relationship with said container.

JOHN E. RQ'I'HROCK.

Closing is effected by applying a disk.

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